In the electrodeposition of tin and lead many methods have been proposed which have, in general, evolved towards methods based on depositing these two metals as alloys from a bath which is known as fluoride or fluoroborate bath. Tin-lead alloys deposited from these baths provide the necessary advantages associated with these deposits.
Another problem for depositing tin and lead from these prior art baths has been the disadvantages associated with maintaining a consistent tin-lead proportion in the deposit as it is being plated from a bath solution. Thus, the prior art bath solutions have been dependent, with respect to the composition of the alloy deposit, not only on the current density (expressed in amperes per square feet, i.e., ASF), but also based on the temperature and concentration of each of the metal elements in the bath solution. Other baths have had a number of organic additives and thus have caused organic contaminant inclusion or occlusion, especially at the high deposit rates (in terms of ASF) sought to be used for economic operation of any plating line.
In addition to the prior art disadvantages arising from the changing alloy deposits, deposit contamination, and the stringent effluent treatment which is required, other disadvantages of the fluoride and fluoroborate bath are associated with fluoride or fluorine corrosion. Toxicity of the components in the prior art fluoride or fluoroborate bath is also a problem. The various shortcomings of the prior art bath have thus prompted a search for the replacement bath having all the advantages but few, if any, disadvantages.